Asked to take his passenger to the National Museum of American Art yesterday noon, the cabdriver replied, "You mean the one on Constitution Avenue?"

It was all the confirmation anyone needed that even the cabdrivers still don't know where the museum is -- despite 22 years at the same location: Eighth and G streets NW.

Hapless fares usually end up on the Mall, at the better-known National Museum of American History.

"There's even a mistake on the Metro map," says NMAA Director Betsy Broun, who was appointed last year and yesterday took her first decisive step toward changing things by inviting all the cabdrivers in town to lunch -- specifically, to drive by the museum between 11 a.m. and 2 p.m. for a free, carry-away sandwich, a drink and a museum souvenir. It was a smash.

By 2, nearly 400 cabbies had been cheerfully greeted by volunteer museum docents; told they were at THE NATIONAL MUSEUM OF AMERICAN ART; offered lemonade or iced tea, and egg salad, ham or tuna sandwiches (or cheese for non-meat-eaters); and invited to have a Polaroid photograph taken of them with the huge sign in front of the building, an offer most happily accepted.

Bertram E. Barton, Comfort Cab 197, said he'd heard about the party on the CB radio: "Everybody's talking about it. I know the museum has been here for a while, but I didn't know the name. I'll remember it now for sure."

Even the occupant of a police car, stopping by to complain about the ballet of U-turns in front of the museum, was assuaged by the army of smiling docents in cowboy hats. He went away happy with his own bag lunch.

"I think it's lovely, yes indeed -- it's beautiful," said Edward Joppy, 632 Yellow, who's been hacking for 23 years and was pleased to pick up a fare with his food. He said he'd been treated to coffee and doughnuts by a few new hotels in town, but never to lunch.

He turned on the air conditioning in his pristine cab. "I want my customers to be real comfortable when I take them to the museum," said Joppy.

And which museum was that, asked his fare? "Write it down for me, would you?" he asked. "I don't want to forget."

Though more than 1,200 announcements had been distributed by museum interns and volunteers through various cab companies and the D.C. Taxicab Commission, it was the radio dispatchers who seemed to bring the largest numbers.

Each driver was also given a small gift with the museum's address on the back: an air freshener shaped like Luis Jimenez's 16 1/2-foot-tall fiberglass sculpture "Vaquero," a cowboy on a bucking bronco, which stands at the museum entrance on G Street. The historic neoclassical building, which occupies two city blocks between Seventh and Ninth and F and G streets NW, is located hard by the Gallery Place Metro stop. The NMAA shares the building with the other "Gallery" for which the subway stop is named: the National Portrait Gallery.

The museum's most triumphant moment came when one cab pulled up with a puzzled passenger, who, after a raucous reception, determined that he was in the wrong place. He was looking for the National Museum of American History.

"At last," said an NMAA staffer, "a mistake in our favor!"

Everyone cheered.